Suburban Furnace Blower

Teamfoxy · 08-12-2018, 06:39 AM

Several times on our current trip, the furnace blower has come on when we are running off battery power. Cool air comes out of all the heating ducts and it runs for a few minutes then stops. The thermostat has not been set to heat and the air temperature has been in the mid to high 80's. It does not run again on the same day that I have noticed.
Does anyone know why this occurs? I cannot see anything in the manual about this. I was first concerned about draining the batteries, but it does not run long enough or often enough to do that.

wmckinley · 08-12-2018, 05:31 PM

Teamfoxy, I've worked on suburban furnaces since my first coach, now on number 5. Analyzing the problem, given my experiences and with the limited information, it sounds like it may be the thermostat is getting flakey. Most of the furnaces use the blue wire from the furnace to the thermostat.Yellow is ground and red is +12. The furnace is designed to start when the blue wire gets a 12v signal from the thermostat. If it is only a momentary pulse on the blue wire, the furnace will completely go thru it's start up sequence. Once the startup sequence is completed, if the signal from the thermostat is still there it will continue to run, If the signal is gone it will shut down. operation explanation done.
Troubleshoot the system by disconnecting the thermostat wiring. If it does not repeat the original noted behavior It's the thermostat, If it does repeat it, there is most likely a wire issue between the thermostat and the furnace.

Teamfoxy · 08-13-2018, 06:18 AM

Thanks Bill!
The momentary impulse from the thermostat and running through the startup makes sense. I am not sure how to realistically troubleshoot the issue by disconnecting the wires because the instances have been days apart. It has happened 3 times over a two month period that we have been on the road. It has only happened when we are on 12V only, but we also dry camped for more than a week without it happening. The Coleman Mach thermostat runs the AC fine.

wmckinley · 08-13-2018, 08:27 AM

Teamfoxy, I have the same thermostat in my coach. You said it only happens when on battery only, pick up a little battery monitor to check your dc voltages. Don't rely on the Monitor panel, it could be your getting into a low house battery condition that may be affecting the thermostat. Let us know if you find a resolution.

Teamfoxy · 08-14-2018, 05:20 AM

The batteries are all brand new, but I can check voltages with my multi-meter. Perhaps there is a bad ground or terminal in/on the furnace circuit? When I first got the coach, the main ground terminal was quite corroded, but I cleaned it all up, replaced the end fittings and sprayed it with corrosion block.

Teamfoxy · 10-30-2018, 05:42 AM

We put off the furnace issue until we got back home since it really wasn't needed. The furnace would not start up when the switch was turned on, but never came on by itself again as described in the opening message.
I downloaded the service manual from Suburban and ran through the trouble shooting guide. While at it, I pulled the furnace, which is not difficult, but not quite so easy as described in the manual. It is pretty snug in the housing. The issue was the control board in the furnace itself, not the thermostat. (although I did replace that too) It is an $80 part and easy to replace once the furnace is out. I also pulled the blower housing and cleaned it out before I began trouble shooting . There was a fairly large mud wasp nest in the furnace side which would have reduced the air flow. It would probably be a good idea to cover the inlet and outlet holes when the RV is stored and I will have to think of a good way to do it.

charge-it · 10-30-2018, 02:18 PM

Quote:

Originally Posted by Teamfoxy

There was a fairly large mud wasp nest in the furnace side which would have reduced the air flow. It would probably be a good idea to cover the inlet and outlet holes when the RV is stored and I will have to think of a good way to do it.

Here's what Camco came up with.

Teamfoxy · 10-31-2018, 04:59 AM

I would prefer to have a cover that also deflects water. The pad at our house tilts away from the side with the furnace, so rainwater can collect in the heat chamber. We would of course remove it to operate the furnace.